A Divalent PAMAM-Based Matrix Metalloproteinase/Carbonic Anhydrase Inhibitor for the Treatment of Dry Eye Syndrome.

Synthetic sulfonamide derivatives are a class of potent matrix metalloproteinase inhibitors (MMPI) that have potential for the treatment of diseases related to uncontrolled expression of these enzymes. The lack of selectivity of the large majority of such inhibitors, leading to the inhibition of MMPs in tissues other than the targeted one, has dramatically reduced the therapeutic interest in MMPIs. The recent development of efficient drug delivery systems that allow the transportation of a selected drug to its site of action has opened the way to new perspectives in the use of MMPIs. Here, a PAMAM-based divalent dendron with two sulfonamidic residues was synthesized. This nanomolar inhibitor binds to the catalytic domain of two MMPs as well as to the transmembrane human carbonic anhydrases (hCAs) XII, which is present in the eye and considered an antiglaucoma target. In the animal model of an experimental dry eye, no occurrence of dotted staining in eyes treated with our inhibitor was observed, indicating no symptoms of corneal desiccation.

Development of an HPLC/UV assay for the evaluation of inhibitors of human recombinant monoacylglycerol lipase.

Monoacylglycerol lipase (MAGL) is a membrane-associated cytosolic serine hydrolase which catalyses the hydrolysis of the endocannabinoid 2-arachidonoylglycerol into arachidonic acid and glycerol. MAGL represents the link between the endocannabinoid and the eicosanoid system indeed its inhibition enhances endocannabinoid signalling and lowers eicosanoid production. Here we present a radioactive-free, sensitive and solid HPLC-UV based method to evaluate MAGL activity by using 4-nitrophenylacetate (4-NPA) as substrate. The enzymatic activity is measured by quantifying the 4-nitrophenol (PNP) (λ = 315 nm) formation on a C18 stationary phase. The method was validated by calculating IC50 values of the reference inhibitors JZL184, CAY10499 and JW642 and confirming the irreversible and non-competitive mechanism of inhibition for JZL184. Furthermore in order to resemble the catalytic conditions of MAGL at cell membrane level, the surfactant Triton X-100 was added, as a micelle forming agent and 4-nitrophenyldodecanoate (4-NPDo) was used as lipophilic substrate for MAGL. The data obtained confirmed that the HPLC method is an alternative, radioactive-free approach for the screening and characterization of new MAGL inhibitors. Finally this assay prevents, in an unequivocal manner, any interference related to the intrinsic absorbance of screened compounds or metabolites generated upon enzymatic cleavage which could seriously affect the assay readout.

4-Methylbenzylidene camphor microspheres: reconstituted epidermis (Skinethic®) permeation and distribution.

OBJECTIVE: The UV filter 3(4-methylbenzylidene) camphor (4-MBC) is a common ingredient in sunscreen cosmetic products. However, different 'in vitro' and 'in vivo' studies suggest that 4-MBC can cause endocrine disrupting effects. Therefore, there is a need for new systems able to minimize the skin penetration of this UV filter. The aim of this study was to evaluate cutaneous permeation and distribution, through and into EPISKIN reconstituted epidermis (RE) from an O/W emulsion containing 4-MBC free or encapsulated in polymeric substantive microspheres. METHODS: Microspheres containing 4-MBC were prepared using the emulsification-solvent evaporation method and characterized for shape and surface morphology and encapsulation efficiency. O/A emulsions containing sunscreen free or encapsulated in microspheres were undergone to permeation tests through RE using vertical diffusion cells. At the end of the in vitro permeation experiments, the skin was subjected to tape stripping procedure to separate stratum corneum from viable epidermis. Each part was properly treated to extract the sunscreen retained and subject to quantitative analysis. RESULTS: The encapsulation of the sunscreen in the microspheres remarkably reduced the permeation of 4-MBC and increased its retention on the skin surface where its action is more desirable. CONCLUSIONS: The results of this study confirm the validity of substantive microspheres as an ideal formulation candidate to use in sunscreen preparation as they appear minimizing its systemic uptake and the potential associate toxicological risks. Therefore, more of the active sunscreen remains on the surface of the skin where it is intended to act and a higher activity it will explicate.

Validation of bovine hoof slices as a model for infected human toenails: in vitro ciclopirox transungual permeation.

BACKGROUND: Topical therapy has recently been proposed for treating onychomycosis and other nail disturbances. However, the clinical outcome may be limited by the difficulty of active ingredients effectively penetrating the nail plate. Bovine hoof membranes have been widely used to predict in vitro efficacy of drug products in nail diseases. Many studies have compared bovine hooves with human healthy nails, considering the difference between healthy and unhealthy nails to be negligible. OBJECTIVES: To validate bovine hoof slices as a model for human unhealthy nails by investigating the transungual permeation/retention of ciclopirox (CPX) through bovine hoof slices and excised infected human toenails after application of a new film-forming formulation (P-3051). To investigate the ability of CPX to achieve fungicidal concentrations in and through infected toenails. METHODS: A new experimental technique based on a permeation unit allowed analysis by high-performance liquid chromatography of the amounts of CPX permeating through and retained in the membranes. The efficacy index was evaluated as follows: amount of permeated CPX/Trichophyton rubrum minimum inhibiting concentration. RESULTS: Extrapolated CPX flux through bovine hoof slices was about 14-fold higher than through infected human toenails, the difference being mainly due to the fourfold higher thickness of the toenails. In toenails, the CPX efficacy index for T. rubrum was positive (>1·0) soon after P-3051 application. CONCLUSIONS: This study confirms the validity of bovine hoof slices as a model for infected human nails, and suggests a substantial equivalence between the two models. Following P-3051 application, CPX reaches fungicidal concentrations in and through human infected toenails.

Optimization of skin permeation and distribution of ibuprofen by using nanostructures (coagels) based on alkyl vitamin C derivatives.

In this investigation two vitamin C-based -6-O-ascorbic acid esters (ASC12 and ASC16), able to form liquid-crystal structures (coagels) was evaluated for their potential usefulness to promote the permeation and distribution of ibuprofen (IBU). Two coagel formulations and the same coagels added of polyethylene glycol (PEG-400) were assayed in comparison with a commercial product (Arfen®) by using hairless rat skin as model. The ASC16 and ASC12 derivatives gave rise to stable supramolecular assemblies in water and in water/PEG mixtures (coagels), allowing the solubilization of IBU (0.85%) and producing a IBU controlled release systems, as evidenced by the dynamic dialyse test: the n values were near 1.0, indicative of a linear kinetic, for all coagel formulations, except for the ASC12PEG/C formulation (n=1.51). Our results evidenced the enhancement activity of coagels and the synergic effect of the combination with PEG: all coagels showed a higher amount of IBU permeated through the skin compared to commercial Arfen® with an enhancement factor of 52.94 and 21.53 for ASC12PEG/C and ASC16/C respectively. Otherwise, coagels formulations appeared to produce a low IBU depot in the skin and in the same order of magnitude in epidermis and derma, in spite of significant increase of IBU cutaneous permeation. The positive synergic effect of the coagel-PEG mixtures was demonstrated by the high amount of IBU accumulated in the upper skin layers. The effect of the coagels on the IBU skin permeation and distribution depending on their hydro-lipophilic character could allow a rational design and an optimization of topical formulations.

Poloxamer 407 microspheres for orotransmucosal drug delivery. Part I: formulation, manufacturing and characterization.

The two-part article aimed to investigate poloxamer 407-based microspheres as a novel platform for enhancing and controlling the delivery of atenolol across the oromucosal tissue. In the Part I of the work, atenolol-loaded poloxamers 407 microparticles were prepared by the solvent free spray congealing technology. This approach was feasible upon the high viscosity of the systems allowing for high loaded (20% w/w) non-aggregated microspheres. Several formulations were studied and the results demonstrated that the drug release patterns, solubility data, mucoadhesion to buccal tissue and gelling properties in saliva could be modified by adding different amount of an amphiphilic polymer-lipid excipient (Gelucire(®) 50/13) to poloxamer 407. Particularly, microspheres based only on poloxamer 407 exhibited very high solubility, mucoadhesive strength and gelling behaviour. To assess their potential as matrix for buccal application, the gelling property and the drug release from tablets obtained from direct compression of the microparticles were further evaluated. The microspheres were then characterized by differential scanning calorimetry, X-ray powder diffraction and Fourier transform-infrared spectra analysis. No solid state modifications and chemical interactions were detectable in the microspheres after manufacturing and during storage, suggesting their stability and use as orotransmucosal delivery systems.

Poloxamer 407 microspheres for orotransmucosal drug delivery. Part II: In vitro/in vivo evaluation.

Aim of this research was to evaluate novel microspheres based on poloxamer 407, alone or in mixture with Gelucire(®) 50/13, as possible buccal delivery system for atenolol (AT). The microspheres have been prepared by spray congealing and investigated to assess AT in vitro delivery through cellulose membranes and ex vivo permeation using porcine buccal mucosa. The microparticles were tested as such or directly compacted to obtain tablets. For comparison the physical mixtures, tablets of the physical mixtures and an AT solution were examined. Finally, the microparticles were sublingually administered in rabbits to evaluate AT pharmacokinetics compared to a market oral tablet (reference). The AT release from microspheres through the synthetic membrane was delayed with respect to the drug solution, more markedly when microparticles contained poloxamer as unique adjuvant; this formulation enhanced AT transmucosal permeation. The enhancement effect of poloxamer was confirmed by the permeation experiments on the corresponding physical mixture. Tabletting hindered both release through cellulose membranes and transmucosal permeation of drug. In vivo studies revealed that the absolute bioavailability of microsphere formulations was higher than that of reference in spite of a lower dosage of drug, suggesting a possible dose reduction by AT microparticles orotransmucosal administration.

Hydrosoluble medicated nail lacquers: in vitro drug permeation and corresponding antimycotic activity.

BACKGROUND: Two nail lacquers, containing ciclopirox (CPX) or amorolfine (MRF), based on water-insoluble polymers are currently considered mainstays of topical treatment of onychomycosis. The present study aimed at evaluating the antimycotic activity of a new water-soluble nail lacquer containing CPX (CPX/sol), easily removable by washing with water and applicable to periungual skin. OBJECTIVES: To compare transungual permeation of CPX with that of MRF in the same hydroxypropyl chitosan-based nail lacquer (MRF/sol) and with a nonwater-soluble reference (Loceryl); Galderma International, La Défense, France), and to evaluate the antimycotic activity of CPX/sol and Loceryl against the most common fungal strains that cause onychomycosis. Methods In vitro drug permeation experiments with CPX/sol, MRF/sol and Loceryl were carried out through bovine hoof slices. Experimental permeates from CPX/sol and Loceryl underwent in vitro susceptibility testing against clinical isolates of dermatophytes, moulds and yeast. Results MRF transungual flux from MRF/sol lacquer was significantly higher when compared with Loceryl. CPX was able to permeate hoof membranes more easily compared with MRF. CPX and MRF concentrations in the subungual fluids collected after application of CPX/sol or Loceryl were sufficient to inhibit fungal growth, with the exception of Candida parapsilosis. Smaller amounts of fluid containing CPX were required for complete inhibition of fungal growth. Efficacy index values were significantly higher for CPX/sol. Conclusions Application of the CPX/sol nail lacquer allows rapid nail penetration of CPX, providing CPX levels sufficient to inhibit fungal growth for a prolonged period of time (30 h) after application of lacquer dose. CPX/sol nail lacquer appeared superior to the market reference Loceryl in terms of both vehicle (hydroxypropyl chitosan) and active ingredient (CPX) as witnessed by its higher efficacy on all nail pathogens.

Niaouli oils from different sources: analysis and influence on cutaneous permeation of estradiol in vitro.

Previous studies in vitro had identified niaouli essential oil (NEO) as a valuable transdermal permeation promoter for estradiol (ES). Subsequent considerations on the complex issue of NEO provenance and composition stimulated the present investigation, which was aimed at defining the composition of NEOs obtained from four different sources, at evaluating their influence on transdermal permeation of ES through hairless mouse skin, and at formulating and evaluating simpler terpene mixtures mimicking the NEOs' composition. While all oils contained 1,8-cineol (eucalyptol) as the main component, appreciable variations in composition could be evidenced, originating differences on the ES cutaneous permeation. Two artificial mixtures containing the same proportions of the main terpenes present in each oil (except the commercially unavailable gamma-terpineol) proved equal or significantly superior in activity when compared with the original oils. It is felt that this study might contribute to the formulation of terpene mixtures acting more efficiently and reproducibly with respect to natural NEOs, whose complex and variable composition, depending on growing place, season, and extraction process, is well documented in the relevant literature.

Skin permeation and distribution of two sunscreens: a comparison between reconstituted human skin and hairless rat skin.

The aims of this work were (a) to develop a simple and reproducible procedure for percutaneous absorption and distribution tests of sunscreens using one human skin culture model (Epiderm 606; reconstructed epidermis, RE), (b) to compare the said model with rat skin (RS) in vitro and (c) to evaluate the effect of different formulations. The cutaneous permeation and distribution of two UV filters, ethylhexylmethoxycinnamate (MC80) and ethylhexyltriazone (T150), using 3 different vehicles were investigated. The permeation studies demonstrated that neither MC80 nor T150 permeated through both RS and RE in spite of different thicknesses of the 2 substrates. Distribution studies demonstrated that sectioning by cryomicrotome to obtain horizontal skin layers was suitable for both RS and RE (apart from its small thickness) with a good reproducibility of data. The amounts of sunscreens retained in the 2 substrates were in the same order of magnitude for all formulations with a greater depot in RS. Different distribution profiles of the tested formulations could be ascribed to the different lipid compositions of RE and RS. Since the physicochemical characteristics of RE are closer to those of human skin, the results obtained with reconstructed human skin models could be suitable to replace human skin in 'in vitro testing'.

Rufloxacin eyedrops: effect of different formulations on ocular pharmacokinetics in rabbits.

PURPOSE: To evaluate the aqueous humor pharmacokinetics of rufloxacin in rabbits after topical administration of different formulations, and to individuate the ones showing the best pharmacokinetic profile. METHODS: Six formulations were instilled in rabbit eyes: two pH 7.2 suspensions of non-salified rufloxacin base, or zwitterion (RUF), one of which was viscosized with tamarind seed polysaccharide (TSP); two pH 7.2 solutions of RUF obtained using hydroxypropyl-beta-cyclodextrin (CD), one of which was viscosized with TSP; and two pH 5.0 solutions of rufloxacin hydrochloride (RUF-HCl ), one of which was viscosized with TSP. At different times after administration, samples of aqueous humor were withdrawn and analyzed by high-pressure liquid chromatography. The main pharmacokinetic parameters of RUF in the aqueous humor produced by the different formulations were calculated and statistical differences were assessed. RESULTS: The best results, in terms of aqueous humor bioavailability, were observed with two TSP-viscosized formulations: a solution of the hydrochloride (TSP/RUF-HCl) and a suspension of the base (TSP/RUF), followed by the non-viscosized solution of RUF-HCl. The formulations containing CD-solubilized RUF were much less effective. CONCLUSIONS: The present data confirm the significant availability-enhancing properties of tamarind seed polysaccharide, and indicate that solubilization of RUF with hydroxypropyl-beta-cyclodextrin (CD/RUF) results in decreased drug availability with respect to standard formulations. Two of the TSP-viscosized formulations (RUF suspension and RUF-HCl solution) produced aqueous humor RUF concentrations in the range of activity against Enterobacteriaceae and Pseudomonas aeruginosa, thus warranting further studies on applications of rufloxacin in ocular therapy.

In vitro transungual permeation of ciclopirox from a hydroxypropyl chitosan-based, water-soluble nail lacquer.

Commercial antimycotic nail lacquers are commonly based on water-insoluble resins. The present study was aimed at evaluating a novel, experimental nail lacquer (P-3051, Polichem SA, Lugano, Switzerland) based on the water-soluble film-forming agent hydroxypropyl chitosan (HPCH). The in vitro permeation of ciclopirox (CPX) from P-3051 and from a commercial, water-insoluble lacquer based on a vinyl resin (Penlac, Aventis Pharma), was investigated using thin membranes obtained from bovine hooves, an accepted model for human nails. Similar CPX permeation fluxes at steady state through the membranes, but significantly different lag times were observed for P-3051 and Penlac, when these were tested as dry films. The formulations thus appeared to influence only the time required by CPX to saturate the membrane, and not the final drug concentration gradient in the membrane. Permeation experiments performed on the same membranes and on hairless mouse skin with P-3051 and with a similar, HPCH-free vehicle (ERV), both tested in liquid form, disproved the possibility that HPCH might act as a permeation enhancer for CPX in either substrate. The possible reasons for the greater efficiency of the HPCH vehicle in terms of CPX transfer from the vehicle itself to the keratin membrane are discussed. This effect might be tentatively attributed to a particular affinity of HPCH for the membrane, resulting in intimate contact and strong adhesion of the HPCH lacquer to the keratin substrate.

Effect of chitosan and of N-carboxymethylchitosan on intraocular penetration of topically applied ofloxacin.

The effects of chitosan hydrochloride (Ch-HCl) and of N-carboxymethylchitosan (CMCh), formulated in ophthalmic solutions, on the ocular pharmacokinetics of ofloxacin were studied in rabbits. The carboxymethylation of a chitosan of high molecular mass (1460 kDa) and deacetylation degree (89.9%) introduced 0.84 N-carboxymethyl groups per repeating unit. Aqueous solutions containing 1% (w/v) of either polymer showed a pseudoplastic rheologic behaviour, and, when instilled in rabbit eyes, produced no irritation. The kinetics of drug disappearance from tear fluid and the profiles of drug concentration in the aqueous humour versus time were determined and interpreted in the light of a pharmacokinetic model and of drug-polymer binding. Ch-HCl significantly enhanced intraocular drug penetration with respect to an isoviscous drug solution containing poly(vinyl alcohol) and to commercial ofloxacin eyedrops. This effect, which resulted in about 190% increase of the peak concentration in the aqueous, was ascribed to an increased corneal permeability. The polyanionic CMCh failed to enhance intraocular drug penetration. It nevertheless increased precorneal drug retention in virtue of its viscosity and of ofloxacin binding. Consequently, the residence time at concentrations higher than the MIC90 and the bioavailability of the antibiotic in the aqueous were increased by about 150 and 240%, respectively, with respect to the reference vehicle.

Ocular toxicity of some corneal penetration enhancers evaluated by electrophysiology measurements on isolated rabbit corneas.

The influence on electrical resistance and membrane potential of rabbit corneas in vitro of some chemicals used as adjuvants in ophthalmic formulations was investigated, in the attempt to correlate changes in electrophysiological properties of the corneal tissue (possibly indicative of toxic/damaging effects to the corneal epithelium), with the promoting effect of the substances on transcorneal permeation in vitro of timolol maleate (TM). The chemicals, tested at different concentrations, were benzalkonium chloride (BAC), sodium ethylenediaminetetraacetate (EDTA), polyoxyethylene-20-stearyl ether (PSE), polyethoxylated castor oil (PCO), deoxycholic acid sodium salt (DC) and cetylpyridinium chloride (CPC). For these substances, definite correlations were found between promoting activity for permeation of TM and modification of electrophysiological parameters. These parameters were in all cases significantly altered by all agents at all concentrations after a 5-h contact. However, after a 1-h contact, 0.001% PSE and CPC did not significantly modify the corneal resistance, while PCO and PSE did not significantly modify the transcorneal potential at the tested concentrations. Only 0.001% PSE, a nonionic surfactant used as solubilizer and emulsifier, active as promoter for TM, did not modify both electrophysiological parameters to a significant extent after 1 h. The results of this study indicate correlations between ocular toxicity, promoting activity for transcorneal permeation of timolol and modification of the electrophysiological parameters.

Effect of iontophoresis on transcorneal permeation 'in vitro' of two beta-blocking agents, and on corneal hydration.

Purpose of the present investigation was to examine the effect of iontophoresis on permeation of two beta-blocking agents, timolol maleate (TM) and betaxolol hydrochloride (BX) across rabbit corneas in vitro. Continuous or pulsed current of variable intensity and duration was applied, and possible corneal damage due to the electric treatment was assessed by measuring the corneal hydration level. The effect of iontophoresis on corneal permeation of the relatively more hydrophilic TM was much greater than the effect on the more lipophilic BX. It was found that for both drugs the iontophoretically driven transcorneal penetration is governed only by current density and overall time of treatment, irrespective of the type of treatment (single or repeated) and of current (constant or pulsed). For both drugs all significant permeation increases due to iontophoresis were invariably accompanied by a significant increased corneal hydration, indicative of damage to the corneal epithelium. Even if the present in vitro data cannot be extrapolated to an in vivo treatment, they confirm the potential risk associated with ocular iontophoresis.

Effect of chitosan on in vitro release and ocular delivery of ofloxacin from erodible inserts based on poly(ethylene oxide).

The effects of chitosan hydrochloride (CH-HCl) on in vitro release of ofloxacin (OFX) from mucoadhesive erodible ocular inserts and on the relevant ocular pharmacokinetics have been studied both to contribute evidence of the ability of CH-HCl to enhance transcorneal penetration of drugs and to increase the therapeutic efficacy of topically applied OFX. Circular inserts of 6 mm in diameter, 0.8-0.9 mm in thickness and 20 mg in weight, medicated with 0.3 mg drug, were prepared by powder compression. The addition of 10, 20 or 30% medicated CH-HCl microparticles, obtained by spray-drying, to formulations based on poly(ethylene oxide) of MW 900 kDa (PEO 900) or 2000 kDa (PEO 2000) produced changes in the insert microstructure which accelerated both insert erosion and OFX release from inserts. The effect was stronger with higher CH-HCl fractions. Of the CH-HCl-containing formulations based on either PEO 900 or PEO 2000, PEO 900-CH-HCl (9:1 w/w) was more suitable for a prolonged OFX release. Following insertion in the lower conjunctival sac of the rabbit's eye, such an insert produced no substantial increase of AUC(eff) (AUC in the aqueous humour for concentrations >MIC(90%)) with respect to inserts based on plain PEO; however, it produced a concentration peak in the aqueous significantly higher than that produced by any of the CH-HCl-free PEO inserts, and well higher than the MIC(90%) for the more resistant ocular pathogens (7 microg/ml vs. 4 microg/ml). It has been argued that the increase was due to the ability of CH-HCl to enhance the transcorneal permeability of the drug.

Effect of different terpene-containing essential oils on permeation of estradiol through hairless mouse skin.

Purpose of the present investigation was to evaluate six terpene-containing essential oils for their capacity to promote permeation of estradiol (ES) through hairless mouse skin in vitro. Tests on cajuput, cardamom, melissa, myrtle, niaouli and orange oil, all used at the 10% w/w concentration in propylene glycol (PG), evidenced niaouli oil (NIA) as the best permeation promoter for ES. Tests on the main terpene components of NIA (1,8 cineole, alpha-pinene, alpha-terpineol and D-limonene), evaluated neat (10% w/w in PG) or in admixture, confirmed the better promoting activity of whole NIA. The present data point to the validity of complex terpene mixtures, such as that composing NIA, as transdermal penetration enhancers for moderately lipophilic drugs like ES.

Ophthalmic vehicles containing polymer-solubilized tropicamide: "in vitro/in vivo" evaluation.

Commercial 1.0% aqueous tropicamide (TR) eyedrops are buffered to pH 4.4-5.0 to produce sufficiently stable solutions of the weakly basic, poorly soluble drug. These acidic solutions, however, are irritants and may induce copious lachrimation, thus reducing the drug bioavailability. The aim of the present study was to evaluate some solubilizing agents for the preparation of 1.0% TR ophthalmic solutions adjusted at physiologically compatible pH, potentially showing increased eye tolerance, activity, and stability when compared with standard commercial eyedrops. The tested solubilizers were two non-ionic surfactants-Tyloxapol (TY) and Cremophor EL (CR) and one polymer, Pluronic P85 (PL). Four stable 1% TR formulations, containing 3% TY, 7.5% CR, 15% PL, or 5% CR + 10% PL were submitted to mydriatic activity tests in rabbits. They improved to a small but statistically significant extent the AUC for mydriatic effect of TR in the test animals when compared with commercial 1.0% TR eyedrops.

Increased corneal hydration induced by potential ocular penetration enhancers: assessment by differential scanning calorimetry (DSC) and by desiccation.

The corneal toxicity of some surfactants of possible use as ocular penetration enhancers was investigated by measuring their effect on hydration of rabbit corneas 'in vitro'. The tested substances were benzalkonium chloride (BAC), cetylpyridinium chloride (CPC), ethylenediaminetetraacetic acid disodium salt (EDTA), polyoxyethylene-20-stearyl ether (Brij 78, PSE), polyethoxylated castor oil (Cremophor EL, PCO) and sodium deoxycholate (DC). Freshly excised corneas, mounted in perfusion cells, were kept in contact for 1 h with solutions of these agents; corneal hydration was then evaluated by measuring: (a) their total (free+bound) water content by desiccation (gravimetric analysis); and (b) their free water content by differential scanning calorimetry (DSC). The DSC measurements also provided a rough quantitative estimate of corneal solutes. All tested agents significantly influenced corneal hydration, evidently as a consequence of alteration of the corneal epithelium. Although a brief contact with the precorneal tissues 'in vivo' may not prove harmful, the use of these compounds as potential ocular permeation enhancers or otherwise as ingredients of topical ocular formulations for long-term use should be considered with caution.

Comparison of the effect of ultrasound and of chemical enhancers on transdermal permeation of caffeine and morphine through hairless mouse skin in vitro.

The effect of ultrasound (US) on permeation of two model drugs, caffeine (CAF) and morphine (MOR), through hairless mouse skin in vitro was compared with that of three chemical enhancers. Low-frequency (40 KHz), low-power (<0.5 W/cm(2)) US was used; the effect of high-frequency US (1.5-3.0 MHz) was also evaluated in the case of CAF. The chemical enhancers, tested in combination with propylene glycol (PG), were benzalkonium chloride (BAC) oleyl alcohol (OA) and alpha-terpineol (TER). The high-frequency US enhancement of CAF transdermal flux was not statistically significant, while low frequency produced a small but significant increase of the enhancement factor. The effect of US on CAF permeation, however, was lower than that produced by chemical enhancers, in particular OA. The effect of low-frequency US on permeation of MOR was significantly greater (about 10-fold) when compared, on the same frequency and intensity basis, with the effect on CAF. The most active chemical enhancer for MOR, OA, had practically the same effect as low-frequency US. Sonicated skin, although showing slight histological changes, recovered its original low permeability characteristics after turning off sonication. Within the tested system, chemical enhancement appears to offer some advantages over low-frequency US.